Methods and Apparatus for Renal Neuromodulation

ABSTRACT

Methods and apparatus are provided for renal neuromodulation using a pulsed electric field to effectuate electroporation or electrofusion. It is expected that renal neuromodulation (e.g., denervation) may, among other things, reduce expansion of an acute myocardial infarction, reduce or prevent the onset of morphological changes that are affiliated with congestive heart failure, and/or be efficacious in the treatment of end stage renal disease. Embodiments of the present invention are configured for percutaneous intravascular delivery of pulsed electric fields to achieve such neuromodulation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/930,863 filed Jun. 28, 2013, which is a continuation of U.S.patent application Ser. No. 13/619,851 filed Sep. 14, 2012, now U.S.Pat. No. 8,548,600, which is a continuation of U.S. patent applicationSer. No. 12/777,892, filed May 11, 2010, which is a continuation of U.S.patent application Ser. No. 11/782,451, filed Jul. 24, 2007, nowabandoned, which is a divisional of U.S. patent application Ser. No.11/129,765, filed May 13, 2005, now U.S. Pat. No. 7,653,438, whichclaims the benefit of U.S. Provisional Patent Application No.60/616,254, filed Oct. 5, 2004, and U.S. Provisional Patent ApplicationNo. 60/624,793, filed Nov. 2, 2004.

U.S. patent application Ser. No. 11/129,765, filed May 13, 2005, nowU.S. Pat. No. 7,653,438 is also a continuation-in-part of U.S. patentapplication Ser. No. 10/408,665, filed Apr. 8, 2003, now U.S. Pat. No.7,162,303, which claims the benefit of U.S. Provisional PatentApplication Nos. (a) 60/370,190, filed Apr. 8, 2002; (b) 60/415,575,filed Oct. 3, 2002; and (c) 60/442,970, filed Jan. 29, 2003. Thedisclosures of these applications are incorporated herein by referencein their entireties.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

TECHNICAL FIELD

The present invention relates to methods and apparatus for renalneuromodulation. More particularly, the present invention relates tomethods and apparatus for achieving renal neuromodulation via a pulsedelectric field and/or electroporation or electrofusion.

BACKGROUND

Congestive Heart Failure (“CHF”) is a condition that occurs when theheart becomes damaged and reduces blood flow to the organs of the body.If blood flow decreases sufficiently, kidney function becomes impairedand results in fluid retention, abnormal hormone secretions andincreased constriction of blood vessels. These results increase theworkload of the heart and further decrease the capacity of the heart topump blood through the kidney and circulatory system.

This reduced capacity further reduces blood flow to the kidney, which inturn further reduces the capacity of the heart. It is believed thatprogressively decreasing perfusion of the kidney is a principalnon-cardiac cause perpetuating the downward spiral of CHF. Moreover, thefluid overload and associated clinical symptoms resulting from thesephysiologic changes are predominant causes for excessive hospitaladmissions, terrible quality of life and overwhelming costs to thehealth care system due to CHF.

While many different diseases may initially damage the heart, oncepresent, CHF is split into two types: Chronic CHF and Acute (orDecompensated-Chronic) CHF. Chronic Congestive Heart Failure is a longerterm, slowly progressive, degenerative disease. Over years, chroniccongestive heart failure leads to cardiac insufficiency. Chronic CHF isclinically categorized by the patient's ability to exercise or performnormal activities of daily living (such as defined by the New York HeartAssociation Functional Class). Chronic CHF patients are usually managedon an outpatient basis, typically with drugs.

Chronic CHF patients may experience an abrupt, severe deterioration inheart function, termed Acute Congestive Heart Failure, resulting in theinability of the heart to maintain sufficient blood flow and pressure tokeep vital organs of the body alive. These Acute CHF deteriorations canoccur when extra stress (such as an infection or excessive fluidoverload) significantly increases the workload on the heart in a stablechronic CHF patient. In contrast to the stepwise downward progression ofchronic CHF, a patient suffering acute CHF may deteriorate from even theearliest stages of CHF to severe hemodynamic collapse. In addition,Acute CHF can occur within hours or days following an Acute MyocardialInfarction (“AMI”), which is a sudden, irreversible injury to the heartmuscle, commonly referred to as a heart attack.

As mentioned, the kidneys play a significant role in the progression ofCHF, as well as in Chronic Renal Failure (“CRF”), End-Stage RenalDisease (“ESRD”), hypertension (pathologically high blood pressure) andother cardio-renal diseases. The functions of the kidney can besummarized under three broad categories: filtering blood and excretingwaste products generated by the body's metabolism; regulating salt,water, electrolyte and acid-base balance; and secreting hormones tomaintain vital organ blood flow. Without properly functioning kidneys, apatient will suffer water retention, reduced urine flow and anaccumulation of waste toxins in the blood and body. These conditionsresulting from reduced renal function or renal failure (kidney failure)are believed to increase the workload of the heart. In a CHF patient,renal failure will cause the heart to further deteriorate as the waterbuild-up and blood toxins accumulate due to the poorly functioningkidneys and, in turn, cause the heart further harm.

The primary functional unit of the kidneys that is involved in urineformation is called the “nephron”. Each kidney consists of about onemillion nephrons. The nephron is made up of a glomerulus and itstubules, which can be separated into a number of sections: the proximaltubule, the medullary loop (loop of Henle), and the distal tubule. Eachnephron is surrounded by different types of cells that have the abilityto secrete several substances and hormones (such as renin anderythropoietin). Urine is formed as a result of a complex processstarting with the filtration of plasma water from blood into theglomerulus. The walls of the glomerulus are freely permeable to waterand small molecules but almost impermeable to proteins and largemolecules. Thus, in a healthy kidney, the filtrate is virtually free ofprotein and has no cellular elements. The filtered fluid that eventuallybecomes urine flows through the tubules. The final chemical compositionof the urine is determined by the secretion into, and re-absorption ofsubstances from, the urine required to maintain homeostasis.

Receiving about 20% of cardiac output, the two kidneys filter about 125ml of plasma water per minute. Filtration occurs because of a pressuregradient across the glomerular membrane. The pressure in the arteries ofthe kidney pushes plasma water into the glomerulus causing filtration.To keep the Glomerulur Filtration Rate (“GFR”) relatively constant,pressure in the glomerulus is held constant by the constriction ordilatation of the afferent and efferent arterioles, the muscular walledvessels leading to and from each glomerulus.

In a CHF patient, the heart will progressively fail, and blood flow andpressure will drop in the patient's circulatory system. During acuteheart failure, short-term compensations serve to maintain perfusion tocritical organs, notably the brain and the heart that cannot surviveprolonged reduction in blood flow. However, these same responses thatinitially aid survival during acute heart failure become deleteriousduring chronic heart failure.

A combination of complex mechanisms contribute to deleterious fluidoverload in CHF. As the heart fails and blood pressure drops, thekidneys cannot function and become impaired due to insufficient bloodpressure for perfusion. This impairment in renal function ultimatelyleads to the decrease in urine output. Without sufficient urine output,the body retains fluids, and the resulting fluid overload causesperipheral edema (swelling of the legs), shortness of breath (due tofluid in the lungs), and fluid retention in the abdomen, among otherundesirable conditions in the patient.

In addition, the decrease in cardiac output leads to reduced renal bloodflow, increased neurohormonal stimulus, and release of the hormone reninfrom the juxtaglomerular apparatus of the kidney. This results in avidretention of sodium and, thus, volume expansion. Increased renin resultsin the formation of angiotensin, a potent vasoconstrictor. Heart failureand the resulting reduction in blood pressure also reduce the blood flowand perfusion pressure through organs in the body other than thekidneys. As they suffer reduced blood pressure, these organs may becomehypoxic, resulting in a metabolic acidosis that reduces theeffectiveness of pharmacological therapy and increases a risk of suddendeath.

This spiral of deterioration that physicians observe in heart failurepatients is believed to be mediated, at least in part, by activation ofa subtle interaction between heart function and kidney function, knownas the renin-angiotensin system. Disturbances in the heart's pumpingfunction results in decreased cardiac output and diminished blood flow.The kidneys respond to the diminished blood flow as though the totalblood volume was decreased, when in fact the measured volume is normalor even increased. This leads to fluid retention by the kidneys andformation of edema, thereby causing the fluid overload and increasedstress on the heart.

Systemically, CHF is associated with an abnormally elevated peripheralvascular resistance and is dominated by alterations of the circulationresulting from an intense disturbance of sympathetic nervous systemfunction. Increased activity of the sympathetic nervous system promotesa downward vicious cycle of increased arterial vasoconstriction(increased resistance of vessels to blood flow) followed by a furtherreduction of cardiac output, causing even more diminished blood flow tothe vital organs.

In CHF via the previously explained mechanism of vasoconstriction, theheart and circulatory system dramatically reduce blood flow to thekidneys. During CHF, the kidneys receive a command from higher neuralcenters via neural pathways and hormonal messengers to retain fluid andsodium in the body. In response to stress on the heart, the neuralcenters command the kidneys to reduce their filtering functions. Whilein the short term, these commands can be beneficial, if these commandscontinue over hours and days they can jeopardize the person's life ormake the person dependent on artificial kidney for life by causing thekidneys to cease functioning.

When the kidneys do not fully filter the blood, a huge amount of fluidis retained in the body, which results in bloating (fluid retention intissues) and increases the workload of the heart. Fluid can penetrateinto the lungs, and the patient becomes short of breath. This odd andself-destructive phenomenon is most likely explained by the effects ofnormal compensatory mechanisms of the body that improperly perceive thechronically low blood pressure of CHF as a sign of temporarydisturbance, such as bleeding.

In an acute situation, the body tries to protect its most vital organs,the brain and the heart, from the hazards of oxygen deprivation.Commands are issued via neural and hormonal pathways and messengers.These commands are directed toward the goal of maintaining bloodpressure to the brain and heart, which are treated by the body as themost vital organs. The brain and heart cannot sustain low perfusion forany substantial period of time. A stroke or a cardiac arrest will resultif the blood pressure to these organs is reduced to unacceptable levels.Other organs, such as the kidneys, can withstand somewhat longer periodsof ischemia without suffering long-term damage. Accordingly, the bodysacrifices blood supply to these other organs in favor of the brain andthe heart.

The hemodynamic impairment resulting from CHF activates severalneurohormonal systems, such as the renin-angiotensin and aldosteronesystem, sympatho-adrenal system and vasopressin release. As the kidneyssuffer from increased renal vasoconstriction, the GFR drops, and thesodium load in the circulatory system increases. Simultaneously, morerenin is liberated from the juxtaglomerular of the kidney. The combinedeffects of reduced kidney functioning include reduced glomerular sodiumload, an aldosterone-mediated increase in tubular reabsorption ofsodium, and retention in the body of sodium and water. These effectslead to several signs and symptoms of the CHF condition, including anenlarged heart, increased systolic wall stress, an increased myocardialoxygen demand, and the formation of edema on the basis of fluid andsodium retention in the kidney. Accordingly, sustained reduction inrenal blood flow and vasoconstriction is directly responsible forcausing the fluid retention associated with CHF.

CHF is progressive, and as of now, not curable. The limitations of drugtherapy and its inability to reverse or even arrest the deterioration ofCHF patients are clear. Surgical therapies are effective in some cases,but limited to the end-stage patient population because of theassociated risk and cost. Furthermore, the dramatic role played bykidneys in the deterioration of CHF patients is not adequately addressedby current surgical therapies.

The autonomic nervous system is recognized as an important pathway forcontrol signals that are responsible for the regulation of bodyfunctions critical for maintaining vascular fluid balance and bloodpressure. The autonomic nervous system conducts information in the formof signals from the body's biologic sensors such as baroreceptors(responding to pressure and volume of blood) and chemoreceptors(responding to chemical composition of blood) to the central nervoussystem via its sensory fibers. It also conducts command signals from thecentral nervous system that control the various innervated components ofthe vascular system via its motor fibers.

Experience with human kidney transplantation provided early evidence ofthe role of the nervous system in kidney function. It was noted thatafter transplant, when all the kidney nerves were totally severed, thekidney increased the excretion of water and sodium. This phenomenon wasalso observed in animals when the renal nerves were cut or chemicallydestroyed. The phenomenon was called “denervation diuresis” since thedenervation acted on a kidney similar to a diuretic medication. Laterthe “denervation diuresis” was found to be associated withvasodilatation of the renal arterial system that led to increased bloodflow through the kidney. This observation was confirmed by theobservation in animals that reducing blood pressure supplying thekidneys reversed the “denervation diuresis”.

It was also observed that after several months passed after thetransplant surgery in successful cases, the “denervation diuresis” intransplant recipients stopped and the kidney function returned tonormal. Originally, it was believed that the “renal diuresis” was atransient phenomenon and that the nerves conducting signals from thecentral nervous system to the kidney were not essential to kidneyfunction. Later discoveries suggested that the renal nerves had aprofound ability to regenerate and that the reversal of “denervationdiuresis” could be attributed to the growth of new nerve fiberssupplying the kidneys with necessary stimuli.

Another body of research focused on the role of the neural control ofsecretion of the hormone renin by the kidney. As was discussedpreviously, renin is a hormone responsible for the “vicious cycle” ofvasoconstriction and water and sodium retention in heart failurepatients. It was demonstrated that an increase or decrease in renalsympathetic nerve activity produced parallel increases and decreases inthe renin secretion rate by the kidney, respectively.

In summary, it is known from clinical experience and the large body ofanimal research that an increase in renal sympathetic nerve activityleads to vasoconstriction of blood vessels supplying the kidney,decreased renal blood flow, decreased removal of water and sodium fromthe body, and increased renin secretion. It is also known that reductionof sympathetic renal nerve activity, e.g., via denervation, may reversethese processes.

It has been established in animal models that the heart failurecondition results in abnormally high sympathetic stimulation of thekidney. This phenomenon was traced back to the sensory nerves conductingsignals from baroreceptors to the central nervous system. Baroreceptorsare present in the different locations of the vascular system. Powerfulrelationships exist between baroreceptors in the carotid arteries(supplying the brain with arterial blood) and sympathetic nervousstimulus to the kidneys. When arterial blood pressure was suddenlyreduced in experimental animals with heart failure, sympathetic toneincreased. Nevertheless, the normal baroreflex likely is not solelyresponsible for elevated renal nerve activity in chronic CHF patients.If exposed to a reduced level of arterial pressure for a prolonged time,baroreceptors normally “reset”, i.e., return to a baseline level ofactivity, until a new disturbance is introduced. Therefore, it isbelieved that in chronic CHF patients, the components of theautonomic-nervous system responsible for the control of blood pressureand the neural control of the kidney function become abnormal. The exactmechanisms that cause this abnormality are not fully understood, but itseffects on the overall condition of the CHF patients are profoundlynegative.

End-Stage Renal Disease is another condition at least partiallycontrolled by renal neural activity. There has been a dramatic increasein patients with ESRD due to diabetic nephropathy, chronicglomerulonephritis and uncontrolled hypertension. Chronic Renal Failureslowly progresses to ESRD. CRF represents a critical period in theevolution of ESRD. The signs and symptoms of CRF are initially minor,but over the course of 2-5 years, become progressive and irreversible.While some progress has been made in combating the progression to, andcomplications of, ESRD, the clinical benefits of existing interventionsremain limited.

It has been known for several decades that renal diseases of diverseetiology (hypotension, infection, trauma, autoimmune disease, etc.) canlead to the syndrome of CRF characterized by systemic hypertension,proteinuria (excess protein filtered from the blood into the urine) anda progressive decline in GFR ultimately resulting in ESRD. Theseobservations suggest that CRF progresses via a common pathway ofmechanisms and that therapeutic interventions inhibiting this commonpathway may be successful in slowing the rate of progression of CRFirrespective of the initiating cause.

To start the vicious cycle of CRF, an initial insult to the kidneycauses loss of some nephrons. To maintain normal GFR, there is anactivation of compensatory renal and systemic mechanisms resulting in astate of hyperfiltration in the remaining nephrons. Eventually, however,the increasing numbers of nephrons “overworked” and damaged byhyperfiltration are lost. At some point, a sufficient number of nephronsare lost so that normal GFR can no longer be maintained. Thesepathologic changes of CRF produce worsening systemic hypertension, thushigh glomerular pressure and increased hyperfiltration. Increasedglomerular hyperfiltration and permeability in CRF pushes an increasedamount of protein from the blood, across the glomerulus and into therenal tubules. This protein is directly toxic to the tubules and leadsto further loss of nephrons, increasing the rate of progression of CRF.This vicious cycle of CRF continues as the GFR drops with loss ofadditional nephrons leading to further hyperfiltration and eventually toESRD requiring dialysis. Clinically, hypertension and excess proteinfiltration have been shown to be two major determining factors in therate of progression of CRF to ESRD.

Though previously clinically known, it was not until the 1980s that thephysiologic link between hypertension, proteinuria, nephron loss and CRFwas identified. In 1990s the role of sympathetic nervous system activitywas elucidated. Afferent signals arising from the damaged kidneys due tothe activation of mechanoreceptors and chemoreceptors stimulate areas ofthe brain responsible for blood pressure control. In response, the brainincreases sympathetic stimulation on the systemic level, resulting inincreased blood pressure primarily through vasoconstriction of bloodvessels. When elevated sympathetic stimulation reaches the kidney viathe efferent sympathetic nerve fibers, it produces major deleteriouseffects in two forms. The kidneys are damaged by direct renal toxicityfrom the release of sympathetic neurotransmitters (such asnorepinephrine) in the kidneys independent of the hypertension.Furthermore, secretion of renin that activates Angiotensin II isincreased, which increases systemic vasoconstriction and exacerbateshypertension.

Over time, damage to the kidneys leads to a further increase of afferentsympathetic signals from the kidney to the brain. Elevated AngiotensinII further facilitates internal renal release of neurotransmitters. Thefeedback loop is therefore closed, which accelerates deterioration ofthe kidneys.

In view of the foregoing, it would be desirable to provide methods andapparatus for the treatment of congestive heart failure, renal disease,hypertension and/or other cardio-renal diseases via renalneuromodulation and/or denervation.

SUMMARY

The present invention provides methods and apparatus for renalneuromodulation (e.g., denervation) using a pulsed electric field (PEF).Several aspects of the invention apply a pulsed electric field toeffectuate electroporation and/or electrofusion in renal nerves, otherneural fibers that contribute to renal neural function, or other neuralfeatures. Several embodiments of the invention are intravascular devicesfor inducing renal neuromodulation. The apparatus and methods describedherein may utilize any suitable electrical signal or field parametersthat achieve neuromodulation, including denervation, and/or otherwisecreate an electroporative and/or electrofusion effect. For example, theelectrical signal may incorporate a nanosecond pulsed electric field(nsPEF) and/or a PEF for effectuating electroporation. One specificembodiment comprises applying a first course of PEF electroporationfollowed by a second course of nsPEF electroporation to induce apoptosisin any cells left intact after the PEF treatment, or vice versa. Analternative embodiment comprises fusing nerve cells by applying a PEF ina manner that is expected to reduce or eliminate the ability of thenerves to conduct electrical impulses. When the methods and apparatusare applied to renal nerves and/or other neural fibers that contributeto renal neural functions, this present inventors believe that urineoutput will increase and/or blood pressure will be controlled in amanner that will prevent or treat CHF, hypertension, renal systemdiseases, and other renal anomalies.

Several aspects of particular embodiments can achieve such results byselecting suitable parameters for the PEFs and/or nsPEFs. Pulsedelectric field parameters can include, but are not limited to, fieldstrength, pulse width, the shape of the pulse, the number of pulsesand/or the interval between pulses (e.g., duty cycle). Suitable fieldstrengths include, for example, strengths of up to about 10,000 V/cm.Suitable pulse widths include, for example, widths of up to about 1second. Suitable shapes of the pulse waveform include, for example, ACwaveforms, sinusoidal waves, cosine waves, combinations of sine andcosine waves, DC waveforms, DC-shifted AC waveforms, RF waveforms,square waves, trapezoidal waves, exponentially-decaying waves,combinations thereof, etc. Suitable numbers of pulses include, forexample, at least one pulse. Suitable pulse intervals include, forexample, intervals less than about 10 seconds. Any combination of theseparameters may be utilized as desired. These parameters are provided forthe sake of illustration and should in no way be considered limiting.Additional and alternative waveform parameters will be apparent.

Several embodiments are directed to percutaneous intravascular systemsfor providing long-lasting denervation to minimize acute myocardialinfarct (“AMI”) expansion and for helping to prevent the onset ofmorphological changes that are affiliated with congestive heart failure.For example, one embodiment of the invention comprises treating apatient for an infarction, e.g., via coronary angioplasty and/orstenting, and performing an intra-arterial pulsed electric field renaldenervation procedure under fluoroscopic guidance. Alternatively, PEFtherapy could be delivered in a separate session soon after the AMI hadbeen stabilized. Renal neuromodulation also may be used as an adjunctivetherapy to renal surgical procedures. In these embodiments, theanticipated increase in urine output and/or control of blood pressureprovided by the renal PEF therapy is expected to reduce the load on theheart to inhibit expansion of the infarct and prevent CHF.

Several embodiments of intravascular pulsed electric field systemsdescribed herein may denervate or reduce the activity of the renalnervous supply immediately post-infarct, or at any time thereafter,without leaving behind a permanent implant in the patient. Theseembodiments are expected to increase urine output and/or control bloodpressure for a period of several months during which the patient's heartcan heal. If it is determined that repeat and/or chronic neuromodulationwould be beneficial after this period of healing, renal PEF treatmentcan be repeated as needed.

In addition to efficaciously treating AMI, several embodiments ofsystems described herein are also expected to treat CHF, hypertension,renal failure, and other renal or cardio-renal diseases influenced oraffected by increased renal sympathetic nervous activity. For example,the systems may be used to treat CHF at any time by advancing the PEFsystem to a treatment site via a vascular structure and then deliveringa PEF therapy to the treatment site. This may, for example, modify alevel of fluid offload.

Embodiments of intravascular PEF systems described herein may be usedsimilarly to angioplasty or electrophysiology catheters which are wellknown in the art. For example, arterial access may be gained through astandard Seldinger Technique, and an arterial sheath optionally may beplaced to provide catheter access. A guidewire may be advanced throughthe vasculature and into the renal artery of the patient, and then anintravascular PEF may be advanced over the guidewire and/or through thesheath into the renal artery. The sheath optionally may be placed beforeinserting the PEF catheter or advanced along with the PEF catheter suchthat the sheath partially or completely covers the catheter.Alternatively, the PEF catheter may be advanced directly through thevasculature without the use of a guide wire and/or introduced andadvanced into the vasculature without a sheath.

In addition to arterial placement, the PEF system may be placed within avein. Venous access may, for example, be achieved via a jugularapproach. PEF systems may be utilized, for example, within the renalartery, within the renal vein or within both the renal artery and therenal vein to facilitate more complete denervation.

After the PEF catheter is positioned within the vessel at a desiredlocation with respect to the target neurons, it is stabilized within thevessel (e.g., braced against the vessel wall) and energy is delivered tothe target nerve or neurons. In one variation, pulsed RF energy isdelivered to the target to create a non-thermal nerve block, reduceneural signaling, or otherwise modulate neural activity. Alternativelyor additionally, cooling, cryogenic, thermal RF, thermal or non-thermalmicrowave, focused or unfocused ultrasound, thermal or non-thermal DC,as well as any combination thereof, may be employed to reduce orotherwise control neural signaling.

In still other embodiments of the invention, other non-renal neuralstructures may be targeted from within arterial or venous conduits inaddition to or in lieu of renal neural structures. For instance, a PEFcatheter can be navigated through the aorta or the vena cava and broughtinto apposition with various neural structures to treat other conditionsor augment the treatment of renal-cardiac conditions. For example, nervebodies of the lumbar sympathetic chain may be accessed and modulated,blocked or ablated, etc., in this manner.

Several embodiments of the PEF systems may completely block or denervatethe target neural structures, or the PEF systems may otherwise modulatethe renal nervous activity. As opposed to a full neural blockade such asdenervation, other neuromodulation produces a less-than-complete changein the level of renal nervous activity between the kidney(s) and therest of the body. Accordingly, varying the pulsed electric fieldparameters will produce different effects on the nervous activity.

In one embodiment of an intravascular pulsed electric field system, thedevice includes one or more electrodes that are configured to physicallycontact a target region of a renal vasculature for delivery of a pulsedelectric field. For example, the device can comprise a catheter havingan expandable helical section and one or more electrodes at the helicalsection. The catheter may be positioned in the renal vasculature whilein a low profile configuration. The expandable section can then beexpanded to contact the inner surface of the vessel wall. Alternatively,the catheter can have one or more expandable helical electrodes. Forexample, first and second expandable electrodes may be positioned withinthe vessel at a desired distance from one another to provide an activeelectrode and a return electrode. The expandable electrodes may compriseshape-memory materials, inflatable balloons, expandable meshes, linkagesystems and other types of devices that can expand in a controlledmanner. Suitable expandable linkage systems include expandable baskets,having a plurality of shape-memory wires or slotted hypotubes, and/orexpandable rings. Additionally, the expandable electrodes may be pointcontact electrodes arranged along a balloon portion of a catheter.

Other embodiments of pulsed electric field systems include electrodesthat do not physically contact the vessel wall. RF energy, bothtraditional thermal energy and relatively non-thermal pulsed RF, areexamples of pulsed electric fields that can be conducted into tissue tobe treated from a short distance away from the tissue itself. Othertypes of pulsed electric fields can also be used in situations in whichthe electrodes do not physically contact the vessel wall. As such, thepulsed electric fields can be applied directly to the nerve via physicalcontact between the electrode contacts and the vessel wall or othertissue, or the pulsed electric fields can be applied indirectly to thenerve without physically contacting the electrode contacts with thevessel wall. The term “nerve contact” accordingly includes physicalcontact of a system element with the nerve and/or tissue proximate tothe nerve, and also electrical contact alone without physicallycontacting the nerve or tissue. To indirectly apply the pulsedelectrical field, the device has a centering element configured toposition the electrodes in a central region of the vessel or otherwisespace the electrodes apart from the vessel wall. The centering elementmay comprise, for example, a balloon or an expandable basket. One ormore electrodes may be positioned on a central shaft of the centeringelement—either longitudinally aligned with the element or positioned oneither side of the element. When utilizing a balloon catheter, theinflated balloon may act as an insulator of increased impedance fororienting or directing a pulsed electric field along a desired electricflow path. As will be apparent, alternative insulators may be utilized.

In another embodiment of the system, a combination apparatus includes anintravascular catheter having a first electrode configured to physicallycontact the vessel wall and a second electrode configured to bepositioned within the vessel but spaced apart from the vessel wall. Forexample, an expandable helical electrode may be used in combination witha centrally-disposed electrode to provide such a bipolar electrode pair.

In yet another embodiment, a radial position of one or more electrodesrelative to a vessel wall may be altered dynamically to focus the pulsedelectric field delivered by the electrode(s). In still anothervariation, the electrodes may be configured for partial or completepassage across the vessel wall. For example, the electrode(s) may bepositioned within the renal vein, then passed across the wall of therenal vein into the perivascular space such that they at least partiallyencircle the renal artery and/or vein prior to delivery of a pulsedelectric field.

Bipolar embodiments of the present invention may be configured fordynamic movement or operation relative to a spacing between the activeand ground electrodes to achieve treatment over a desired distance,volume or other dimension. For example, a plurality of electrodes may bearranged such that a bipolar pair of electrodes can move longitudinallyrelative to each other for adjusting the separation distance between theelectrodes and/or for altering the location of treatment. One specificembodiment includes a first electrode coupled to a catheter and amoveable second electrode that can move through a lumen of the catheter.In alternative embodiments, a first electrode can be attached to acatheter and a second electrode can be attached to anendoluminally-delivered device such that the first and second electrodesmay be repositioned relative to one another to alter a separationdistance between the electrodes. Such embodiments may facilitatetreatment of a variety of renal vasculature anatomies.

Any of the embodiments of the present invention described hereinoptionally may be configured for infusing agents into the treatment areabefore, during or after energy application. The infused agents can beselected to enhance or modify the neuromodulatory effect of the energyapplication. The agents can also protect or temporarily displacenon-target cells, and/or facilitate visualization.

Several embodiments of the present invention may comprise detectors orother elements that facilitate identification of locations for treatmentand/or that measure or confirm the success of treatment. For example,the system can be configured to also deliver stimulation waveforms andmonitor physiological parameters known to respond to stimulation of therenal nerves. Based on the results of the monitored parameters, thesystem can determine the location of renal nerves and/or whetherdenervation has occurred. Detectors for monitoring of such physiologicalresponses include, for example, Doppler elements, thermocouples,pressure sensors, and imaging modalities (e.g., fluoroscopy,intravascular ultrasound, etc.). Alternatively, electroporation may bemonitored directly using, for example, Electrical Impedance Tomography(“EIT”) or other electrical impedance measurements. Additionalmonitoring techniques and elements will be apparent. Such detector(s)may be integrated with the PEF systems or they may be separate elements.

Still other specific embodiments include electrodes configured to alignthe electric field with the longer dimension of the target cells. Forinstance, nerve cells tend to be elongate structures with lengths thatgreatly exceed their lateral dimensions (e.g., diameter). By aligning anelectric field so that the directionality of field propagationpreferentially affects the longitudinal aspect of the cell rather thanthe lateral aspect of the cell, it is expected that lower fieldstrengths can to be used to kill or disable target cells. This isexpected to conserve the battery life of implantable devices, reducecollateral effects on adjacent structures, and otherwise enhance theability to modulate the neural activity of target cells.

Other embodiments of the invention are directed to applications in whichthe longitudinal dimensions of cells in tissues overlying or underlyingthe nerve are transverse (e.g., orthogonal or otherwise at an angle)with respect to the longitudinal direction of the nerve cells. Anotheraspect of these embodiments is to align the directionality of the PEFsuch that the field aligns with the longer dimensions of the targetcells and the shorter dimensions of the non-target cells. Morespecifically, arterial smooth muscle cells are typically elongate cellswhich surround the arterial circumference in a generally spiralingorientation so that their longer dimensions are circumferential ratherthan running longitudinally along the artery. Nerves of the renalplexus, on the other hand, run along the outside of the artery generallyin the longitudinal direction of the artery. Therefore, applying a PEFwhich is generally aligned with the longitudinal direction of the arteryis expected to preferentially cause electroporation in the target nervecells without affecting at least some of the non-target arterial smoothmuscle cells to the same degree. This may enable preferentialdenervation of nerve cells (target cells) in the adventitia orperiarterial region from an intravascular device without affecting thesmooth muscle cells of the vessel to an undesirable extent.

BRIEF DESCRIPTION OF THE DRAWINGS

Several embodiments of the present invention will be apparent uponconsideration of the following detailed description, taken inconjunction with the accompanying drawings, in which like referencecharacters refer to like parts throughout, and in which:

FIG. 1 is a schematic view illustrating human renal anatomy.

FIG. 2 is a schematic detail view showing the location of the renalnerves relative to the renal artery.

FIGS. 3A and 3B are schematic side- and end-views, respectively,illustrating a direction of electrical current flow for selectivelyaffecting renal nerves.

FIG. 4 is a schematic side-view, partially in section, of anintravascular catheter having a plurality of electrodes in accordancewith one embodiment of the invention.

FIG. 5 is a schematic side-view, partially in section, of anintravascular device having a pair of expanding helical electrodesarranged at a desired distance from one another in accordance withanother embodiment of the invention.

FIG. 6 is a schematic side-view, partially in section, of anintravascular device having a first electrode on an expandable balloon,and a second electrode on a catheter shaft in accordance with anotherembodiment of the invention.

FIG. 7 is a schematic side-view, partially in section, of anintravascular device having an expanding first electrode deliveredthrough the lumen of a catheter and a complementary second electrodecarried by the catheter in accordance with another embodiment of theinvention.

FIG. 8 is a schematic side-view, partially in section, of anintravascular device having an expandable basket and a plurality ofelectrodes at the basket in accordance with another embodiment of theinvention.

FIG. 9 is a schematic detail view of the apparatus of FIG. 8illustrating one embodiment of the electrodes in accordance with anotherembodiment of the invention.

FIG. 10 is a schematic side-view, partially in section, of anintravascular device having expandable ring electrodes for contactingthe vessel wall and an optional insulation element in accordance withanother embodiment of the invention.

FIGS. 11A-11C are schematic detail views of embodiments of differentwindings for the ring electrodes of FIG. 10.

FIG. 12 is a schematic side-view, partially in section, of anintravascular device having ring electrodes of FIG. 10 with the windingsshown in FIGS. 11A-11C.

FIG. 13 is a schematic side-view, partially in section, of anintravascular device having a ring electrode and a luminally-deliveredelectrode in accordance with another embodiment of the invention.

FIG. 14 is a schematic side-view, partially in section, of anintravascular device having a balloon catheter and expandable pointcontact electrodes arranged proximally and distally of the balloon inaccordance with another embodiment of the invention.

FIG. 15 is a schematic side-view of an intravascular device having aballoon catheter and electrodes arranged proximally and distally of theballoon in accordance with another embodiment of the invention.

FIGS. 16A and 16B are schematic side-views, partially in section,illustrating stages of a method of using the apparatus of FIG. 15 inaccordance with an embodiment of the invention.

FIG. 17 is a schematic side-view of an intravascular device having aballoon catheter and a plurality of dynamically operable electrodes inaccordance with another embodiment of the invention.

FIG. 18 is a schematic side-view of an intravascular device having adistal electrode deployed through a lumen of the balloon catheter inaccordance with another embodiment of the invention.

FIGS. 19A and 19B are side-views, partially in section, illustratingmethods of using the intravascular device shown in FIG. 18 to modulaterenal neural activity in patients with various renal vasculatures.

FIG. 20 is a side view, partially in section, illustrating anintravascular device having a plurality of electrodes arranged along theshaft of, and in line with, a centering element in accordance withanother embodiment of the invention.

FIG. 21 is a side-view, partially in section, illustrating anintravascular device having electrodes configured for dynamic radialrepositioning to facilitate focusing of a pulsed electric field inaccordance with another embodiment of the invention.

FIG. 22 is a side-view, partially in section, of an intravascular devicehaving an infusion/aspiration catheter in accordance with anotherembodiment of the invention.

FIGS. 23A-23C are, respectively, a side-view, partially in section, andcross-sectional views along section line A-A of FIG. 23A, illustrating amethod of using an intravascular device in accordance with an embodimentof the invention configured for passage of electrode(s) at leastpartially across the vessel wall.

FIGS. 24A and 24B are side-views, partially in section, illustrating anintravascular device having detectors for measuring or monitoringtreatment efficacy in accordance with another embodiment of theinvention.

DETAILED DESCRIPTION A. Overview

The present invention relates to methods and apparatus for renalneuromodulation and/or other neuromodulation. More particularly, thepresent invention relates to methods and apparatus for renalneuromodulation using a pulsed electric field to effectuateelectroporation or electrofusion. As used herein, electroporation andelectropermeabilization are methods of manipulating the cell membrane orintracellular apparatus. For example, short high-energy pulses causepores to open in cell membranes. The extent of porosity in the cellmembrane (e.g., size and number of pores) and the duration of the pores(e.g., temporary or permanent) are a function of the field strength,pulse width, duty cycle, field orientation, cell type and otherparameters. In general, pores will generally close spontaneously upontermination of lower strength fields or shorter pulse widths (hereindefined as “reversible electroporation”). Each cell type has a criticalthreshold above which pores do not close such that pore formation is nolonger reversible; this result is defined as “irreversibleelectroporation,” “irreversible breakdown” or “irreversible damage.” Atthis point, the cell membrane ruptures and/or irreversible chemicalimbalances caused by the high porosity occur. Such high porosity can bethe result of a single large hole and/or a plurality of smaller holes.Certain types of electroporation energy parameters also appropriate foruse in renal neuromodulation are high voltage pulses with a duration inthe sub-microsecond range (nanosecond pulsed electric fields, or nsPEF)which may leave the cellular membrane intact, but alter theintracellular apparatus or function of the cell in ways which cause celldeath or disruption. Certain applications of nsPEF have been shown tocause cell death by inducing apoptosis, or programmed cell death, ratherthan acute cell death. Also, the term “comprising” is used throughout tomean including at least the recited feature such that any greater numberof the same feature and/or additional types features are not precluded.

Several embodiments of the present invention provide intravasculardevices for inducing renal neuromodulation, such as a temporary changein target nerves that dissipates over time, continuous control overneural function, and/or denervation. The apparatus and methods describedherein may utilize any suitable electrical signal or field parameters,e.g., any electric field, that will achieve the desired neuromodulation(e.g., electroporative effect). To better understand the structures ofthe intravascular devices and the methods of using these devices forneuromodulation, it is useful to understand the renal anatomy in humans.

B. Selected Embodiments of Methods for Neuromodulation

With reference now to FIG. 1, the human renal anatomy includes kidneys Kthat are supplied with oxygenated blood by renal arteries RA, which areconnected to the heart by the abdominal aorta AA. Deoxygenated bloodflows from the kidneys to the heart via renal veins RV and the inferiorvena cava IVC. FIG. 2 illustrates a portion of the renal anatomy ingreater detail. More specifically, the renal anatomy also includes renalnerves RN extending longitudinally along the lengthwise dimension L ofrenal artery RA generally within the adventitia of the artery. The renalartery RA has smooth muscle cells SMC that surround the arterialcircumference spiral around the angular axis θ of the artery, i.e.,around the circumference of the artery. The smooth muscle cells of therenal artery accordingly have a lengthwise or longer dimension extendingtransverse (i.e., non-parallel) to the lengthwise dimension of the renalartery. The misalignment of the lengthwise dimensions of the renalnerves and the smooth muscle cells is defined as “cellularmisalignment.”

Referring to FIGS. 3A and 3B, the cellular misalignment of the renalnerves and the smooth muscle cells may be exploited to selectivelyaffect renal nerve cells with reduced effect on smooth muscle cells.More specifically, because larger cells require less energy to exceedthe irreversibility threshold of electroporation, several embodiments ofelectrodes of the present invention are configured to align at least aportion of an electric field generated by the electrodes with or nearthe longer dimensions of the cells to be affected. In specificembodiments, the intravascular device has electrodes configured tocreate an electrical field aligned with or near the lengthwise dimensionof the renal artery RA to affect renal nerves RN. By aligning anelectric field so that the field preferentially affects the lengthwiseaspect of the cell rather than the diametric or radial aspect of thecell, lower field strengths may be used to necrose cells. As mentionedabove, this is expected to reduce power consumption and mitigate effectson non-target cells in the electric field.

Similarly, the lengthwise or longer dimensions of tissues overlying orunderlying the target nerve are orthogonal or otherwise off-axis (e.g.,transverse) with respect to the longer dimensions of the nerve cells.Thus, in addition to aligning the PEF with the lengthwise or longerdimensions of the target cells, the PEF may propagate along the lateralor shorter dimensions of the non-target cells (i.e. such that the PEFpropagates at least partially out of alignment with non-target smoothmuscle cells SMC). Therefore, as seen in FIGS. 3A and 3B, applying a PEFwith propagation lines Li generally aligned with the longitudinaldimension L of the renal artery RA is expected to preferentially causeelectroporation, electrofusion, denervation or other neuromodulation incells of the target renal nerves RN without unduly affecting thenon-target arterial smooth muscle cells SMC. The pulsed electric fieldmay propagate in a single plane along the longitudinal axis of the renalartery, or may propagate in the longitudinal direction along any angularsegment θ through a range of 0°-360°.

Embodiments of the method shown in FIGS. 3A and 3B may have particularapplication with the intravascular methods and apparatus of the presentinvention. For instance, a PEF catheter placed within the renal arterymay propagate an electric field having a longitudinal portion that isaligned to run with the longitudinal dimension of the artery in theregion of the renal nerves RN and the smooth muscle cell SMC of thevessel wall so that the wall of the artery remains at leastsubstantially intact while the outer nerve cells are destroyed.

C. Embodiments of Systems and Additional Methods for Neuromodulation

FIG. 4 shows one embodiment of an intravascular pulsed electric fieldapparatus 200 in accordance with the present invention that includes oneor more electrodes configured to physically contact a target regionwithin the renal vasculature and deliver a pulsed electric field acrossa wall of the vasculature. The apparatus 200 is shown within a patient'srenal artery RA, but it can be positioned in other intravascularlocations (e.g., the renal vein). This embodiment of the apparatus 200comprises an intravascular catheter 210 having a proximal section 211 a,a distal section 211 b, and a plurality of distal electrodes 212 at thedistal section 211 b. The proximal section 211 a generally has anelectrical connector to couple the catheter 210 to a pulse generator,and the distal section 211 b in this embodiment has a helicalconfiguration. The apparatus 200 is electrically coupled to a pulsedelectric field generator 100 located proximal and external to thepatient; the electrodes 212 are electrically coupled to the generatorvia catheter 210. The generator 100 may be utilized with any embodimentof the present invention described hereinafter for delivery of a PEFwith desired field parameters. It should be understood that electrodesof embodiments described hereinafter may be connected to the generator,even if the generator is not explicitly shown or described with eachvariation.

The helical distal section 211 b of catheter 210 is configured to apposethe vessel wall and bring electrodes 212 into close proximity toextra-vascular neural structures. The pitch of the helix can be variedto provide a longer treatment zone, or to minimize circumferentialoverlap of adjacent treatments zones in order to reduce a risk ofstenosis formation. This pitch change can be achieved by combining aplurality of catheters of different pitches to form catheter 210, or byadjusting the pitch of catheter 210 through the use of internal pullwires, adjusting mandrels inserted into the catheter, shaping sheathsplaced over the catheter, or by any other suitable means for changingthe pitch either in-situ or before introduction into the body.

The electrodes 212 along the length of the pitch can be individualelectrodes, a common but segmented electrode, or a common and continuouselectrode. A common and continuous electrode may, for example, comprisea conductive coil formed into or placed over the helical portion ofcatheter 210. A common but segmented electrode may, for example, beformed by providing a slotted tube fitted onto or into the helicalportion of the catheter, or by electrically connecting a series ofindividual electrodes.

Individual electrodes or groups of electrodes 212 may be configured toprovide a bipolar signal, or all or a subset of the electrodes may beused together in conjunction with a separate external patient ground formonopolar use (the ground pad may, for example, be placed on thepatient's leg). Electrodes 212 may be dynamically assignable tofacilitate monopolar and/or bipolar energy delivery between any of theelectrodes and/or between any of the electrodes and an external ground.

Catheter 210 may be delivered to renal artery RA in a low profiledelivery configuration within sheath 150. Once positioned within theartery, the catheter may self-expand or may be expanded actively, e.g.,via a pull wire or a balloon, into contact with an interior wall of theartery. A pulsed electric field then may be generated by the PEFgenerator 100, transferred through catheter 210 to electrodes 212, anddelivered via the electrodes 212 across the wall of the artery. In manyapplications, the electrodes are arranged so that the pulsed electricfield is aligned with the longitudinal dimension of the artery tomodulate the neural activity along the renal nerves (e.g., denervation).This may be achieved, for example, via irreversible electroporation,electrofusion and/or inducement of apoptosis in the nerve cells.

FIG. 5 illustrates an apparatus 220 for neural modulation in accordancewith another embodiment of the invention. The apparatus 220 includes apair of catheters 222 a and 222 b having expandable distal sections 223a and 223 b with helical electrodes 224 a and 224 b, respectively. Thehelical electrodes 224 a and 224 b are spaced apart from each other by adesired distance within a patient's renal vasculature. Electrodes 224a-b may be actuated in a bipolar fashion such that one electrode is anactive electrode and the other is a return electrode. The distancebetween the electrodes may be altered as desired to change the fieldstrength and/or the length of nerve segment modulated by the electrodes.The expandable helical electrodes may comprise shape-memory propertiesthat facilitate self-expansion, e.g., after passage through sheath 150,or the electrodes may be actively expanded into contact with the vesselwall, e.g., via an inflatable balloon or via pull wires, etc. Thecatheters 222 a-b preferably are electrically insulated in areas otherthan the distal helices of electrodes 224 a-b.

FIG. 6 illustrates an apparatus 230 comprising a balloon catheter 232having expandable balloon 234, a helical electrode 236 arranged aboutthe balloon 234, and a shaft electrode 238 on the shaft of catheter 232.The shaft electrode 238 can be located proximal of expandable balloon234 as shown, or the shaft electrode 238 can be located distal of theexpandable balloon 234.

When the apparatus 230 is delivered to a target vessel, e.g., withinrenal artery RA, the expandable balloon 234 and the helical electrode236 are arranged in a low profile delivery configuration. As seen inFIG. 6, once the apparatus has been positioned as desired, expandableballoon 234 may be inflated to drive the helical electrode 236 intophysical contact with the wall of the vessel. In this embodiment, theshaft electrode 238 does not physically contact the vessel wall.

It is well known in the art of both traditional thermal RF energydelivery and of relatively non-thermal pulsed RF energy delivery thatenergy may be conducted to tissue to be treated from a short distanceaway from the tissue itself. Thus, it may be appreciated that “nervecontact” comprises both physical contact of a system element with anerve, as well as electrical contact alone without physical contact, ora combination of the two. A centering element optionally may be providedto place electrodes in a central region of the vessel. The centeringelement may comprise, for example, an expandable balloon, such asballoon 234 of apparatus 230, or an expandable basket as describedhereinafter. One or more electrodes may be positioned on a central shaftof the centering element—either longitudinally aligned with the elementor positioned on one or both sides of the element—as is shaft electrode238 of apparatus 230. When utilizing a balloon catheter such as catheter232, the inflated balloon may act as an insulator of increased impedancefor directing a pulsed electric field along a desired electric flowpath. As will be apparent, alternative insulators may be utilized.

As seen in FIG. 6, when the helical electrode 236 physically contactsthe wall of renal artery RA, the generator 100 may generate a PEF suchthat current passes between the helical electrode 236 and the shaftelectrode 238 in a bipolar fashion. The PEF travels between theelectrodes along lines Li that generally extend along the longitudinaldimension of the artery. The balloon 234 locally insulates and/orincreases the impedance within the patient's vessel such that the PEFtravels through the wall of the vessel between the helical and shaftelectrodes. This focuses the energy to enhance denervation and/or otherneuromodulation of the patient's renal nerves, e.g., via irreversibleelectroporation.

FIG. 7 illustrates an apparatus 240 similar to those shown in FIGS. 4-6in accordance with another embodiment of the invention. The apparatus240 comprises a balloon catheter 242 having an expandable balloon 244and a shaft electrode 246 located proximal of the expandable balloon244. The apparatus 240 further comprises an expandable helical electrode248 configured for delivery through a guidewire lumen 243 of thecatheter 242. The helical electrode 248 shown in FIG. 7 isself-expanding.

As seen in FIG. 7, after positioning the catheter 242 in a target vessel(e.g. renal artery RA), the balloon 244 is inflated until it contactsthe wall of the vessel to hold the shaft electrode 246 at a desiredlocation within the vessel and to insulate or increase the impedance ofthe interior of the vessel. The balloon 244 is generally configured toalso center the shaft electrode 246 within the vessel or otherwise spacethe shaft electrode apart from the vessel wall by a desired distance.After inflating the balloon 244, the helical electrode 248 is pushedthrough lumen 243 until the helical electrode 248 extends beyond thecatheter shaft; the electrode 248 then expands or otherwise moves intothe helical configuration to physically contact the vessel wall. Abipolar pulsed electric field may then be delivered between the helicalelectrode 248 and the shaft electrode 246 along lines Li. For example,the helical electrode 248 may comprise the active electrode and theshaft electrode 246 may comprise the return electrode, or vice versa.

With reference now to FIG. 8, apparatus comprising an expandable baskethaving a plurality of electrodes that may be expanded into contact withthe vessel wall is described. Apparatus 250 comprises catheter 252having expandable distal basket 254 formed from a plurality ofcircumferential struts or members. A plurality of electrodes 256 areformed along the members of basket 254. Each member of the basketillustratively comprises a bipolar electrode pair configured to contacta wall of renal artery RA or another desired blood vessel.

Basket 254 may be fabricated, for example, from a plurality ofshape-memory wires or ribbons, such as Nitinol, spring steel or elgiloywires or ribbons, that form basket members 253. When the basket memberscomprise ribbons, the ribbons may be moved such that a surface areacontacting the vessel wall is increased. Basket members 253 are coupledto catheter 252 at proximal and distal connections 255 a and 255 b,respectively. In such a configuration, the basket may be collapsed fordelivery within sheath 150, and may self-expand into contact with thewall of the artery upon removal from the sheath. Proximal and/or distalconnection 255 a and 255 b optionally may be configured to translatealong the shaft of catheter 252 for a specified or unspecified distancein order to facilitate expansion and collapse of the basket.

Basket 254 alternatively may be formed from a slotted and/or laser-cuthypotube. In such a configuration, catheter 252 may, for example,comprise inner and outer shafts that are moveable relative to oneanother. Distal connection 255 b of basket 254 may be coupled to theinner shaft and proximal connection 255 a of the basket may be coupledto the outer shaft. Basket 254 may be expanded from a collapsed deliveryconfiguration to the deployed configuration of FIG. 8 by approximatingthe inner and outer shafts of catheter 252, thereby approximating theproximal and distal connections 255 a and 255 b of the basket andexpanding the basket. Likewise, the basket may be collapsed byseparating the inner and outer shafts of the catheter.

As seen in FIG. 9, individual electrodes may be arranged along a basketstrut or member 253. In one embodiment, the strut is formed from aconductive material coated with a dielectric material, and theelectrodes 256 may be formed by removing regions of the dielectriccoating. The insulation optionally may be removed only along a radiallyouter surface of the member such that electrodes 256 remain insulated ontheir radially interior surfaces; it is expected that this will directthe current flow outward into the vessel wall.

In addition, or as an alternative, to the fabrication technique of FIG.9, the electrodes may be affixed to the inside surface, outside surfaceor embedded within the struts or members of basket 254. The electrodesplaced along each strut or member may comprise individual electrodes, acommon but segmented electrode, or a common and continuous electrode.Individual electrodes or groups of electrodes may be configured toprovide a bipolar signal, or all or a subset of the electrodes may beactuated together in conjunction with an external patient ground formonopolar use.

One advantage of having electrodes 256 contact the vessel wall as shownin the embodiment of FIG. 8 is that it may reduce the need for aninsulating element, such as an expandable balloon, to achieve renaldenervation or other neuromodulation. However, it should be understoodthat such an insulating element may be provided and, for example,expanded within the basket. Furthermore, having the electrodes contactthe wall may provide improved field geometry, i.e., may provide anelectric field more aligned with the longitudinal axis of the vessel.Such contacting electrodes also may facilitate stimulation of the renalnerves before, during or after neuromodulation to better position thecatheter 252 before treatment or for monitoring the effectiveness oftreatment.

In a variation of apparatus 250, electrodes 256 may be disposed alongthe central shaft of catheter 252, and basket 254 may simply center theelectrodes within the vessel to facilitate more precise delivery ofenergy across the vessel wall. This configuration may be well suited toprecise targeting of vascular or extra-vascular tissue, such as therenal nerves surrounding the renal artery. Correctly sizing the basketor other centering element to the artery provides a known distancebetween the centered electrodes and the arterial wall that may beutilized to direct and/or focus the electric field as desired. Thisconfiguration may be utilized in high-intensity focused ultrasound ormicrowave applications, but also may be adapted for use with any otherenergy modality as desired.

Referring now to FIG. 10, it is expected that electrodes forming acircumferential contact with the wall of the renal artery may providefor more complete renal denervation or renal neuromodulation. In FIG.10, a variation of the present invention comprising ring electrodes isdescribed. Apparatus 260 comprises catheter 262 having expandable ringelectrodes 264 a and 264 b configured to contact the wall of the vessel.The electrodes may be attached to the shaft of catheter 262 via struts266, and catheter 262 may be configured for delivery to renal artery RAthrough sheath 150 in a low profile configuration. Struts 266 may beself-expanding or may be actively or mechanically expanded. Catheter 262comprises guidewire lumen 263 for advancement over a guidewire. Catheter262 also comprises optional inflatable balloon 268 that may act as aninsulating element of increased impedance for preferentially directingcurrent flow that is traveling between electrodes 264 a and 264 b acrossthe wall of the artery.

FIGS. 11A-11C illustrate various embodiments of windings for ringelectrodes 264. As shown, the ring electrodes may, for example, be woundin a coil (FIG. 11A), a zigzag (FIG. 11B) or a serpentine configuration(FIG. 11C). The periodicity of the winding may be specified, as desired.Furthermore, the type of winding, the periodicity, etc., may vary alongthe circumference of the electrodes.

With reference to FIG. 12, a variation of apparatus 260 is describedcomprising ring electrodes 264 a′ and 264 b′ having a sinusoidal windingin one embodiment of the serpentine winding shown in FIG. 11C. Struts266 illustratively are attached to apexes of the sinusoid. The windingof electrodes 264 a′ and 264 b′ may provide for greater contact areaalong the vessel wall than do electrodes 264 a and 264 b, while stillfacilitating sheathing of apparatus 260 within sheath 150 for deliveryand retrieval.

FIG. 13 illustrates another variation of apparatus 260 comprising aproximal ring electrode 264 a, and further comprising a distal electrode270 delivered through guidewire lumen 263 of catheter 262. The distalelectrode 270 is non-expanding and is centered within the vessel viacatheter 262. The distal electrode 270 may be a standard guide wirewhich is connected to the pulsed electric field generator and used as anelectrode. However, it should be understood that electrode 270alternatively may be configured for expansion into contact with thevessel wall, e.g., may comprise a ring or helical electrode.

Delivering the distal electrode through the lumen of catheter 262 mayreduce a delivery profile of apparatus 260 and/or may improveflexibility of the device. Furthermore, delivery of the distal electrodethrough the guidewire lumen may serve as a safety feature that ensuresthat the medical practitioner removes any guidewire disposed withinlumen 263 prior to delivery of a PEF. It also allows for customizationof treatment length, as well as for treatment in side branches, asdescribed hereinafter.

Ring electrodes 264 a and 264 b and 264 a′ and 264 b′ optionally may beelectrically insulated along their radially inner surfaces, while theirradially outer surfaces that contact the vessel wall are exposed. Thismay reduce a risk of thrombus formation and also may improve or enhancethe directionality of the electric field along the longitudinal axis ofthe vessel. This also may facilitate a reduction of field voltagenecessary to disrupt neural fibers. Materials utilized to at leastpartially insulate he ring electrodes may comprise, for example, PTFE,ePTFE, FEP, chronoprene, silicone, urethane, Pebax, etc. With referenceto FIG. 14, another variation of apparatus 260 is described, wherein thering electrodes have been replaced with point electrodes 272 disposed atthe ends of struts 266. The point electrodes may be collapsed withstruts 266 for delivery through sheath 150 and may self-expand with thestruts into contact with the vessel wall. In FIG. 14, catheter 262illustratively comprises four point electrodes 272 on either side ofballoon 268. However, it should be understood that any desired number ofstruts and point electrodes may be provided around the circumference ofcatheter 262.

In FIG. 14, apparatus 260 illustratively comprises four struts 266 andfour point electrodes 272 on either side of balloon 268. By utilizingall of the distally disposed electrodes 272 b as active electrodes andall proximal electrodes 272 a as return electrodes, or vice versa, linesLi along which the electric field propagates may be aligned with thelongitudinal axis of a vessel. A degree of line Li overlap along therotational axis of the vessel may be specified by specifying the angularplacement and density of point electrodes 272 about the circumference ofthe catheter, as well as by specifying parameters of the PEF.

With reference now to FIG. 15, another variation of an intravascular PEFcatheter is described. Apparatus 280 comprises catheter 282 havingoptional inflatable balloon or centering element 284, shaft electrodes286 a and 286 b disposed along the shaft of the catheter on either sideof the balloon, as well as optional radiopaque markers 288 disposedalong the shaft of the catheter, illustratively in line with theballoon. Balloon 284 serves as both a centering element for electrodes286 and as an electrical insulator for directing the electric field, asdescribed previously.

Apparatus 280 may be particularly well-suited for achieving precisetargeting of desired arterial or extra-arterial tissue, since properlysizing balloon 284 to the target artery sets a known distance betweencentered electrodes 286 and the arterial wall that may be utilized whenspecifying parameters of the PEF. Electrodes 286 alternatively may beattached to balloon 284 rather than to the central shaft of catheter 282such that they contact the wall of the artery. In such a variation, theelectrodes may be affixed to the inside surface, outside surface orembedded within the wall of the balloon.

Electrodes 286 arranged along the length of catheter 282 can beindividual electrodes, a common but segmented electrode, or a common andcontinuous electrode. Furthermore, electrodes 286 may be configured toprovide a bipolar signal, or electrodes 286 may be used together orindividually in conjunction with a separate patient ground for monopolaruse.

Referring now to FIGS. 16A and 16B, a method of using apparatus 280 toachieve renal denervation is described. As seen in FIG. 16A, catheter282 may be disposed at a desired location within renal artery RA,balloon or centering element 284 may be expanded to center electrodes286 a and 286 b and to optionally provide electrical insulation, and aPEF may be delivered, e.g., in a bipolar fashion between the proximaland distal electrodes 286 a and 286 b. It is expected that the PEF willachieve renal denervation and/or neuromodulation along treatment zoneone T₁. If it is desired to modulate neural activity in other parts ofthe renal artery, balloon 284 may be at least partially deflated, andthe catheter may be positioned at a second desired treatment zone T₂, asin FIG. 16B. The medical practitioner optionally may utilizefluoroscopic imaging of radiopaque markers 288 to orient catheter 282 atdesired locations for treatment. For example, the medical practitionermay use the markers to ensure a region of overlap O between treatmentzones T₁ and T₂, as shown.

With reference to FIG. 17, a variation of apparatus 280 is describedcomprising a plurality of dynamically controllable electrodes 286 a and286 b disposed on the proximal side of balloon 284. In one variation,any one of proximal electrodes 286 a may be energized in a bipolarfashion with distal electrode 286 b to provide dynamic control of thelongitudinal distance between the active and return electrodes. Thisalters the size and shape of the zone of treatment. In anothervariation, any subset of proximal electrodes 286 a may be energizedtogether as the active or return electrodes of a bipolar electric fieldestablished between the proximal electrodes and distal electrode 286 b.

Although the apparatus 280 shown in FIG. 17 has three proximalelectrodes 286 a ₁, 286 a ₂ and 286 a ₃, it should be understood thatthe apparatus 280 can have any alternative number of proximalelectrodes. Furthermore, the apparatus 280 can have a plurality ofdistal electrodes 286 b in addition, or as an alternative, to multipleproximal electrodes. Additionally, one electrode of a pair may becoupled to the catheter 282, and the other electrode may be deliveredthrough a lumen of the catheter, e.g., through a guidewire lumen. Thecatheter and endoluminally-delivered electrode may be repositionedrelative to one another to alter a separation distance between theelectrodes. Such a variation also may facilitate treatment of a varietyof renal vasculature anatomies.

In the variations of apparatus 280 described thus far, distal electrode286b is coupled to the shaft of catheter 282 distal of balloon 284. Thedistal electrode may utilize a lumen within catheter 282, e.g., forrouting of a lead wire that acts as ground. Additionally, the portion ofcatheter 282 distal of balloon 284 is long enough to accommodate thedistal electrode.

Catheters commonly are delivered over metallic and/or conductiveguidewires. In many interventional therapies involving catheters,guidewires are not removed during treatment. As apparatus 280 isconfigured for delivery of a pulsed electric field, if the guidewire isnot removed, there may be a risk of electric shock to anyone in contactwith the guidewire during energy delivery. This risk may be reduced byusing polymer-coated guidewires.

With reference to FIG. 18, another variation of apparatus 280 isdescribed wherein distal electrode 286 b of FIGS. 16 and 17 has beenreplaced with a distal electrode 270 configured to be moved through alumen of the catheter as described previously with respect to FIG. 13.As will be apparent, proximal electrode 286 a alternatively may bereplaced with the luminally-delivered electrode, such that electrodes286 b and 270 form a bipolar electrode pair. Electrode 270 does notutilize an additional lumen within catheter 282, which may reduceprofile. Additionally, the length of the catheter distal of the balloonneed not account for the length of the distal electrode, which mayenhance flexibility. Furthermore, the guidewire must be exchanged forelectrode 270 prior to treatment, which reduces a risk of inadvertentelectrical shock. In one variation, electrode 270 optionally may be usedas the guidewire over which catheter 282 is advanced into position priorto delivery of the PEF, thereby obviating a need for exchange of theguidewire for the electrode. Alternatively, a standard metallicguidewire may be used as the electrode 270 simply by connecting thestandard guidewire to the pulsed electric field generator. The distalelectrode 270 may be extended any desired distance beyond the distal endof catheter 282. This may provide for dynamic alteration of the lengthof a treatment zone. Furthermore, this might facilitate treatment withindistal vasculature of reduced diameter.

With reference to FIGS. 19A and 19B, it might be desirable to performtreatments within one or more vascular branches that extend from a mainvessel, for example, to perform treatments within the branches of therenal artery in the vicinity of the renal hilum. Furthermore, it mightbe desirable to perform treatments within abnormal or less commonbranchings of the renal vasculature, which are observed in a minority ofpatients. As seen in FIG. 19A, distal electrode 270 may be placed insuch a branch of renal artery RA, while catheter 282 is positionedwithin the main branch of the artery. As seen in FIG. 19B, multipledistal electrodes 270 might be provided and placed in various common oruncommon branches of the renal artery, while the catheter remains in themain arterial branch.

Referring to FIG. 20, yet another variation of an intravascular PEFcatheter is described. Apparatus 290 comprises catheter 292 having aplurality of shaft electrodes 294 disposed in line with centeringelement 296. Centering element 296 illustratively comprises anexpandable basket, such as previously described expandable basket 254 ofFIG. 8. However, it should be understood that the centering elementalternatively may comprise a balloon or any other centering element.Electrodes 294 may be utilized in a bipolar or a monopolar fashion.

Referring now to FIG. 21, another variation of the invention isdescribed comprising electrodes configured for dynamic radialrepositioning of one or more of the electrodes relative to a vesselwall, thereby facilitating focusing of a pulsed electric field deliveredby the electrodes. Apparatus 300 comprises catheter 302 havingelectrodes 304 disposed in line with nested expandable elements. Thenested expandable elements comprise an inner expandable element 306 andan outer expandable centering element 308. Electrodes 304 are disposedalong the inner expandable element, while the outer expandable centeringelement is configured to center and stabilize catheter 302 within thevessel. Inner element 306 may be expanded to varying degrees, as desiredby a medical practitioner, to dynamically alter the radial positions ofelectrodes 304. This dynamic radial repositioning may be utilized tofocus energy delivered by electrodes 304 such that it is delivered totarget tissue.

Nested elements 306 and 308 may comprise a balloon-in-balloonarrangement, a basket-in-basket arrangement, some combination of aballoon and a basket, or any other expandable nested structure. In FIG.21, inner expandable element 306 illustratively comprises an expandablebasket, while outer expandable centering element 308 illustrativelycomprises an expandable balloon. Electrodes 302 are positioned along thesurface of inner balloon 306.

Any of the variations of the present invention described hereinoptionally may be configured for infusion of agents into the treatmentarea before, during or after energy application, for example, to enhanceor modify the neurodestructive or neuromodulatory effect of the energy,to protect or temporarily displace non-target cells, and/or tofacilitate visualization. Additional applications for infused agentswill be apparent. If desired, uptake of infused agents by cells may beenhanced via initiation of reversible electroporation in the cells inthe presence of the infused agents. Infusion may be especially desirablewhen a balloon centering element is utilized. The infusate may comprise,for example, saline or heparinized saline, protective agents, such asPoloxamer-188, or anti-proliferative agents. Variations of the presentinvention additionally or alternatively may be configured foraspiration. For example, infusion ports or outlets may be provided on acatheter shaft adjacent a centering device, the centering device may beporous (for instance, a “weeping” balloon), or basket struts may be madeof hollow hypotubes and slotted or perforated to allow infusion oraspiration.

With reference to FIG. 22, a variation of the present inventioncomprising an infusion/aspiration PEF catheter is described. Apparatus310 comprises catheter 312 having proximal and distal inflatableballoons 314 a and 314 b, respectively. Proximal shaft electrode 316a isdisposed between the balloons along the shaft of catheter 312, whiledistal electrode 316 b is disposed distal of the balloons along thecatheter shaft. One or more infusion or aspiration holes 318 aredisposed along the shaft of catheter 312 between the balloons inproximity to proximal electrode 316 a.

Apparatus 310 may be used in a variety of ways. In a first method ofuse, catheter 312 is disposed within the target vessel, such as renalartery RA, at a desired location. One or both balloons 314 are inflated,and a protective agent or other infusate is infused through hole(s) 318between the balloons in proximity to electrode 316 a. A PEF suitable forinitiation of reversible electroporation is delivered across electrodes316 to facilitate uptake of the infusate by non-target cells within thevessel wall. Delivery of the protective agent may be enhanced by firstinflating distal balloon 314 b, then infusing the protective agent,which displaces blood, then inflating proximal balloon 314 a.

Remaining infusate optionally may be aspirated such that it isunavailable during subsequent PEF application when irreversibleelectroporation of nerve cells is initiated. Aspiration may be achievedby at least partially deflating one balloon during aspiration.Alternatively, aspiration may be achieved with both balloons inflated,for example, by infusing saline in conjunction with the aspiration toflush out the vessel segment between the inflated balloons. Such bloodflushing may reduce a risk of clot formation along proximal electrode316 a during PEF application. Furthermore, flushing during energyapplication may cool the electrode and/or cells of the wall of theartery. Such cooling of the wall cells might protect the cells fromirreversible electroporative damage, possibly reducing a need forinfusion of a protective agent.

After infusion and optional aspiration, a PEF suitable for initiation ofirreversible electroporation in target nerve cells may be deliveredacross electrodes 316 to denervate or to modulate neural activity. In analternative method, infusion of a protective agent may be performedduring or after initiation of irreversible electroporation in order toprotect non-target cells. The protective agent may, for example, plug orfill pores formed in the non-target cells via the irreversibleelectroporation.

In another alternative method, a solution of chilled (i.e., less thanbody temperature) heparinized saline may be simultaneously infused andaspirated between the inflated balloons to flush the region between theballoons and decrease the sensitivity of vessel wall cells toelectroporation. This is expected to further protect the cells duringapplication of the PEF suitable for initiation of irreversibleelectroporation. Such flushing optionally may be continuous throughoutapplication of the pulsed electric field. A thermocouple or othertemperature sensor optionally may be positioned between the balloonssuch that a rate of chilled infusate infusion may be adjusted tomaintain a desired temperature. The chilled infusate preferably does notcool the target tissue, e.g., the renal nerves. A protective agent, suchas Poloxamer-188, optionally may be infused post-treatment as an addedsafety measure.

Infusion alternatively may be achieved via a weeping balloon catheter.Further still, a cryoballoon catheter having at least one electrode maybe utilized. The cryoballoon may be inflated within a vessel segment tolocally reduce the temperature of the vessel segment, for example, toprotect the segment and/or to induce thermal apoptosis of the vesselwall during delivery of an electric field. The electric field may, forexample, comprise a PEF or a thermal, non-pulsed electric field, such asa thermal RF field.

Referring now to FIGS. 23A, 23B and 23C, a variation of a PEF catheterconfigured for passage of electrode(s) at least partially across thevessel wall is described. For example, the electrode(s) may bepositioned within the renal vein and then passed across the wall of therenal vein such that they are disposed in Gerota's or renal fascia andnear or at least partially around the renal artery. In this manner, theelectrode(s) may be positioned in close proximity to target renal nervefibers prior to delivery of a pulsed electric field.

As seen in FIG. 23A, apparatus 320 comprises catheter 322 having needleports 324 and centering element 326, illustratively an inflatableballoon. Catheter 322 also optionally may comprise radiopaque markers328. Needle ports 324 are configured for passage of needles 330therethrough, while needles 330 are configured for passage of electrodes340.

Renal vein RV runs parallel to renal artery RA. An imaging modality,such as intravascular ultrasound, may be used to identify the positionof the renal artery relative to the renal vein. For example,intravascular ultrasound elements optionally may be integrated intocatheter 322. Catheter 322 may be positioned within renal vein RV usingwell-known percutaneous techniques, and centering element 326 may beexpanded to stabilize the catheter within the vein. Needles 330 then maybe passed through catheter 322 and out through needle ports 324 in amanner whereby the needles penetrate the wall of the renal vein andenter into Gerota's or renal fascia F. Radiopaque markers 328 may bevisualized with fluoroscopy to properly orient needle ports 324 prior todeployment of needles 330.

Electrodes 340 are deployed through needles 330 to at least partiallyencircle renal artery RA, as in FIGS. 23A and 23B. Continued advancementof the electrodes may further encircle the artery, as in FIG. 23C. Withthe electrodes deployed, stimulation and/or PEF electroporationwaveforms may be applied to denervate or modulate the renal nerves.Needles 330 optionally may be partially or completely retracted prior totreatment such that electrodes 340 encircle a greater portion of therenal artery. Additionally, a single electrode 340 may be providedand/or actuated in order to provide a monopolar PEF.

Infusate optionally may be infused from needles 330 into fascia F tofacilitate placement of electrodes 340 by creating a space for placementof the electrodes. The infusate may comprise, for example, fluids,heated or chilled fluids, air, CO₂, saline, contrast agents, gels,conductive fluids or any other space-occupying material—be it gas, solidor liquid. Heparinized saline also may be injected. Saline or hypertonicsaline may enhance conductivity between electrodes 340. Additionally oralternatively, drugs and/or drug delivery elements may be infused orplaced into the fascia through the needles.

After treatment, electrodes 340 may be retracted within needles 330, andneedles 330 may be retracted within catheter 322 via needle ports 324.Needles 330 preferably are small enough that minimal bleeding occurs andhemostasis is achieved fairly quickly. Balloon centering element 326optionally may remain inflated for some time after retrieval of needles330 in order to block blood flow and facilitate the clotting process.Alternatively, a balloon catheter may be advanced into the renal veinand inflated after removal of apparatus 320.

Referring to FIGS. 24A and 24B, variations of the invention comprisingdetectors or other elements for measuring or monitoring treatmentefficacy are described. Variations of the invention may be configured todeliver stimulation electric fields, in addition to denervating ormodulating PEFs. These stimulation fields may be utilized to properlyposition the apparatus for treatment and/or to monitor the effectivenessof treatment in modulating neural activity. This may be achieved bymonitoring the responses of physiologic parameters known to be affectedby stimulation of the renal nerves. Such parameters comprise, forexample, renin levels, sodium levels, renal blood flow and bloodpressure. Stimulation also may be used to challenge the denervation formonitoring of treatment efficacy: upon denervation of the renal nerves,the known physiologic responses to stimulation should no longer occur inresponse to such stimulation.

Efferent nerve stimulation waveforms may, for example, comprisefrequencies of about 1-10 Hz, while afferent nerve stimulation waveformsmay, for example, comprise frequencies of up to about 50 Hz. Waveformamplitudes may, for example, range up to about 50V, while pulsedurations may, for example, range up to about 20 milliseconds. When thenerve stimulation waveforms are delivered intravascularly, as in severalembodiments of the present invention, field parameters such asfrequency, amplitude and pulse duration may be modulated to facilitatepassage of the waveforms through the wall of the vessel for delivery totarget nerves. Furthermore, although exemplary parameters forstimulation waveforms have been described, it should be understood thatany alternative parameters may be utilized as desired.

The electrodes used to deliver PEFs in any of the previously describedvariations of the present invention also may be used to deliverstimulation waveforms to the renal vasculature. Alternatively, thevariations may comprise independent electrodes configured forstimulation. As another alternative, a separate stimulation apparatusmay be provided.

One way to use stimulation to identify renal nerves is to stimulate thenerves such that renal blood flow is affected—or would be affected ifthe renal nerves had not been denervated or modulated. Stimulation actsto reduce renal blood flow, and this response may be attenuated orabolished with denervation. Thus, stimulation prior to neural modulationwould be expected to reduce blood flow, while stimulation after neuralmodulation would not be expected to reduce blood flow to the same degreewhen utilizing similar stimulation parameters and location(s) as priorto neural modulation. This phenomenon may be utilized to quantify anextent of renal neuromodulation. Variations of the present invention maycomprise elements for monitoring renal blood flow or for monitoring anyof the other physiological parameters known to be affected by renalstimulation.

In FIG. 24A, a variation of apparatus 280 of FIG. 16 is described havingan element for monitoring of renal blood flow. Guidewire 350 havingDoppler ultrasound sensor 352 has been advanced through the lumen ofcatheter 282 for monitoring blood flow within renal artery RA. Dopplerultrasound sensor 352 is configured to measure the velocity of flowthrough the artery. A flow rate then may be calculated according to theformula:

Q=VA  (1)

where Q equals flow rate, V equals flow velocity and A equalscross-sectional area. A baseline of renal blood flow may be determinedvia measurements from sensor 352 prior to delivery of a stimulationwaveform, then stimulation may be delivered between electrodes 286 a and286 b, preferably with balloon 284 deflated. Alteration of renal bloodflow from the baseline, or lack thereof, may be monitored with sensor352 to identify optimal locations for neuromodulation and/or denervationof the renal nerves.

FIG. 24B illustrates a variation of the apparatus of FIG. 24A, whereinDoppler ultrasound sensor 352 is coupled to the shaft of catheter 282.Sensor 352 illustratively is disposed proximal of balloon 284, but itshould be understood that the sensor alternatively may be disposeddistal of the balloon.

In addition or as an alternative to intravascular monitoring of renalblood flow via Doppler ultrasound, such monitoring optionally may beperformed from external to the patient whereby renal blood flow isvisualized through the skin (e.g., using an ultrasound transducer). Inanother variation, one or more intravascular pressure transducers may beused to sense local changes in pressure that may be indicative of renalblood flow. As yet another alternative, blood velocity may bedetermined, for example, via thermodilution by measuring the time lagfor an intravascular temperature input to travel between points of knownseparation distance.

For example, a thermocouple may be incorporated into, or provided inproximity to, each electrode 286 a and 286 b, and chilled (i.e., lowerthan body temperature) fluid or saline may be infused proximally of thethermocouple(s). A time lag for the temperature decrease to registerbetween the thermocouple(s) may be used to quantify flowcharacteristic(s). A baseline estimate of the flow characteristic(s) ofinterest may be determined prior to stimulation of the renal nerves andmay be compared with a second estimate of the characteristic(s)determined after stimulation.

Commercially available devices optionally may be utilized to monitortreatment. Such devices include, for example, the SmartWire™, F1oWire™and WaveWire™ devices available from Volcano™ Therapeutics Inc., ofRancho Cordova, Calif., as well as the PressureWire® device availablefrom RADI Medical Systems AB of Uppsala, Sweden. Additional commerciallyavailable devices will be apparent. An extent of electroporationadditionally or alternatively may be monitored directly using ElectricalImpedance Tomography (“EIT”) or other electrical impedance measurements,such as an electrical impedance index.

Although preferred illustrative variations of the present invention aredescribed above, it will be apparent to those skilled in the art thatvarious changes and modifications may be made thereto without departingfrom the invention. For example, although the variations primarily havebeen described for use in combination with pulsed electric fields, itshould be understood that any other electric field may be delivered asdesired. It is intended in the appended claims to cover all such changesand modifications that fall within the true spirit and scope of theinvention.

1-23. (canceled)
 24. A method, comprising: intravascularly advancing anelongate shaft of a catheter to renal vasculature of a human patient;locating a first neuromodulation element of the catheter within a distalportion of a main renal artery directly connected to an aorta of thepatient and extending distally toward a kidney of the patient; locatinga second neuromodulation element of the catheter within a branch vesselof the renal artery distal to a bifurcation at a distal end of the mainrenal artery; modulating nerve tissue within an anatomical regionextending about the distal portion of the main renal artery via thefirst neuromodulation element; and modulating nerve tissue within ananatomical region extending about the branch vessel via the secondneuromodulation element.
 25. The method of claim 24 whereinintravascularly advancing an elongate shaft of a catheter to renalvasculature comprises delivering the catheter over a guidewire, andwherein the first neuromodulation element assumes a preformedspiral/helical configuration within the distal portion of the main renalartery when the guidewire is retracted.
 26. The method of claim 24wherein intravascularly advancing an elongate shaft of a catheter torenal vasculature comprises delivering the catheter within a sheath, andwherein the first neuromodulation element assumes a preformedspiral/helical configuration within the distal portion of the main renalartery when removed from the sheath.
 27. The method of claim 24 whereinthe second neuromodulation element is operably connected to the shaft.28. The method of claim 24 wherein the second neuromodulation elementcomprises at least one wire electrode, and wherein locating the secondneuromodulation element of the catheter within the branch vesselcomprises delivering the second neuromodulation element to the branchvessel in a low-profile state and transforming the secondneuromodulation element to an expanded state within the branch vessel.29. The method of claim 24 wherein the second neuromodulation elementcomprises multiple wire electrodes, and wherein locating the secondneuromodulation element of the catheter within the branch vesselcomprises locating a first wire electrode within a first branch vesseland a second wire electrode within a second, different branch vessel.30. The method of claim 24 wherein the first neuromodulation elementfurther comprises a balloon, and wherein locating the firstneuromodulation element of the catheter within the distal portion of themain renal artery comprises inflating the balloon before modulatingnerve tissue via the first neuromodulation element.
 31. The method ofclaim 24 wherein the second neuromodulation element further comprises aballoon, and wherein locating the second neuromodulation element of thecatheter within the branch vessel comprises inflating the balloon beforemodulating nerve tissue via the second neuromodulation element.
 32. Themethod of claim 24 wherein the branch vessel is modulated before themain renal artery is modulated.
 33. The method of claim 24 wherein themain renal artery is modulated before the branch vessel is modulated.34. The method of claim 24 wherein the main renal artery and the branchvessel are modulated simultaneously.
 35. A method for treating a humanpatient diagnosed with a measurable physiological parameter associatedwith systemic sympathetic overactivity or hyperactivity, the methodcomprising: ablating renal nerves within an anatomical region extendingabout a branch renal vessel of the patient, wherein the branch renalvessel is located distal to a bifurcation in a main renal artery of thepatient; and ablating renal nerves within an anatomical region extendingcircumferentially around the main renal artery of the patient, whereinablating the renal nerves results in a decrease in renal sympatheticneural activity in the patient.
 36. The method of claim 35 whereinablating the renal nerves results in a therapeutically beneficialreduction in clinical symptoms of hypertension in the patient.
 37. Themethod of claim 35 wherein ablating the renal nerves comprisessystemically reducing sympathetic tone in the patient.